Kirk: Have I ever mentioned you play a very irritating game of chess, Mr. Spock? Spock: Irritating? [smiling] Ah, yes. One of your Earth emotions. [Kirk considers Spock for a moment, then calmly moves one of his own chess pieces. Spock's smile fades and he frowns as he realizes the effect of Kirk's move] Kirk: Certain you don't know what irritation is? Spock: The fact one of my ancestors married a human female... Kirk: Terrible having bad blood like that. "Star Trek: The Original Series: Where No Man Has Gone Before, Season 1"